#pragma GCC optimize ("O3")
#pragma GCC target ("avx")
#pragma GCC optimize ("Ofast")
#include <cstdio>
#include <cctype>
#include <algorithm>
#include <utility>
#include <vector>
#include <set>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)

inline int gc()noexcept { return getchar_unlocked(); }
inline int input()noexcept {
	int v = 0; char c = gc();
	for (; isdigit(c); c = gc()) {
		v *= 10;
		v += c - '0';
	}
	return v;
}

inline int input_time()noexcept {
	return input() * 1440 + input() * 60 + input();
}
int main() {
	int n = input(), m = input();
	vector<pair<int, int>> range(m);
	rep(i, m) {
		range[i].second = input_time();
		range[i].first = input_time();
	}
	sort(range.begin(), range.end());

	multiset<int> s;
	s.insert(range.front().first);
	int ans = 1;
	FOR(i, 1, m) {
		if (*s.begin() < range[i].second) {
			s.erase(prev(s.lower_bound(range[i].second)));
			s.insert(range[i].first);
			ans++;
		} else if (*s.begin() >= range[i].second && s.size() < n) {
			s.insert(range[i].first);
			ans++;
		}
	}
	printf("%d\n", ans);
}